Sexual diagnosis of skeletons is of importance to physical and forensic anthropologists. The present study attempts to provide a basis from which one might choose a variable of a long bone that is most suitable in sexual assessments of skeletal material. A total of 47 variables of the humerus, radius, ulna, femur, and tibia of 64 recent-modern Japanese (32 male, 32 female) were investigated. The data were analyzed using the t-test and the stepwise discriminant analysis. The width of the articular surface of the distal humerus, the sagittal head diameter of the radius, the diaphyseal cross-section area or the articular breadth of the ulna, the bicondylar width or the transverse diameter of the lateral condyle of the femur, and the proximal epiphyseal breadth of the tibia were useful in sexual diagnosis of each of the long bones. Total accuracies of sex determination using these variables ranged from 91 to 95%. Among these measurements, sexual dimorphism tended to be greatest in the breadth diameters of the elbow and knee joints.